Process of making silica gel



Patented Oct. 16, 1928.

UNITED: STATES PATENT OFFICE.

max nusmcx, or NEWARK, mw .nmsny.

raoonss or MAKING srmca can No Drawing.

V This invention relates to a process of making silica gel, andhas'among its objects the production of a material having highefliciency and capacity by a method which is easy, convenient andc eap.

Silica gel finds extensive use as an adsorbent forgasefs,- vapors,mixtures of gases and vaporsfandgaseous substances. It is also employedin many chemical reactions as a catalyst.

In preparing this gel a solution of a soluble silicate, preferablysodium silicate or ordinary water glass, is treated with ammoniumcarbonate, producing a colloidal solution of silicic a still acid andthey probable reaction being:

(NH CO +Na SiO,'+H O= 7 2NH +Na CO +H,SiO, The silicic acid colloid isallowed to set tov thoroughl to remove the salts adhering thereto andthen dried. The resulting material is a hard, glassy, porous mass andtranslucent to transparent depending on the amount of water held in thepores and the freedom from contaminating salts and other foreign matter.

The silica gel, when properly prepared, has a very porous structure, ishard and stable, and adsorbs gases, vapors and gaseous substancesreadily. Due to its selective adsorbing action it may be used forremoving one .or more constituents from gaseous mixtures. i

. The specific proportions of materials used in my process is notimportant, it being desirable, however, liitions as possibleconsistent'with the complete reaction taking place between the reactmgmaterial's; Satisfactory results may be obtained by using one part ofcommercial sodium silicate (having a specific gravity of about 1.4)diluted withabout four parts of 'w-ater'and to which is 10 per centsolution of ammonium carbonate, with constant stirring.

Although I prefer to use ammonium car bonate or reaction with thesoluble silicate, I do'not desire to be limited thereto, because othersubstances which will react withthe soluble silicate, free thesilicic'acid-therefrom '-may be effected therein to work with asstrong'so-' added one part of a Application filed March 10, 1922. SerialNo. 542,744.-

and yield an alkaline liquor, for exam le ammonium salts such asammonium icarbonate, ammonium chloride, acetate, tartrate, nitrate,etc., may be substituted without departing from the spirit and scope ofthis invention.

The precipitation of the silicious material i may be conducted atmoderate temperature, if desired, but if higher temperatures areemployed, there will be more rapid setting of the gel.

In drying the gel, I prefer to start at a low temperature and raise thetemperature slowly and gradually so that nearly all of the and thestructure of Water will be driven off the gel become stabilized beforethe subjected to the high temperatures.

I may employ the two-stage drying method and may also use a vacuum toassist in the drying, but I have found that no special advantages are tobe derived either from the two-stage drying or from the use of vacuumover my preferred process of raising the temperature continuously andgradually during the drying. This'slow, gradual drying avoids theformation of strains gel is and stresses in the gel lumps into which it"1s brokenu before drying, so that on subsequent igmtion, the lumpswillnot fiyapart and crumble to a powder.

The present invention is not limited to the specific details set forthin the foregoing examples which should be construed as illustrative andnot by way of limitation, and

inview of the numerous modifications which without departing from thespirit and scopeof this invention, it is desired that only suchlimitations be imposed 'as are indicated in the appendedclaims.

I claim as my invention 1. In a process of preparing silica gel,

setting free silicic acid and forming a colloidal solution'thereof byadding to a solution of a' soluble silicate a sufficient quantity of anammonium-salt which will react therewith, free the silicic'acidtherefrom and yield an alkaline liquor, allowing the silicic acid'togelinthe presence of the alkaline liquor of preparing silica gel,

. resulting. in the reaction, washing and then silicic acid therefromand yield an alkaline sufiicient quantity'flof (NI-I CO thoroughly.liquor, allowing the silicic acid to gel in the stirring the substancesat the mixing, allowpresence of the alkaline liquor resulting in ing thesilicic acid to gel in the presence of the reaction, washing and thendrying the the alkaline liquor resulting in the reaction, 15 gel. YWashing and then ing the gel.

3, In aprocess of preparing silica gel, set- 5. In a process 0preparingsilica gel, I ting free all the silicic acid from a solublesetting free silicic acid and forming a colloi-. silicate by adding to asolution thereot a dial solution thereof by addingto a solutionsufficient quantity of (NH) C0 allowing of a soluble silicate asufficient quantity of a the silicic acid to "gel in the presence of thecarbonate of ammonia, allowing the sili'cic alkaline liquor resulting inthe reaction, acid togel in the resence of the alkaline washing and thendrying the gel. liquor resulting in the reaction, washing and 4. In aprocess of preparing silica gel, then drying the gel.

' setting free all the silicic acid from a soluble i Y I 15 silicate byadding to a solution thereof a MAX YABLICK.

